Acoustical panel

ABSTRACT

An acoustical panel, as disclosed, comprises a woven fabric having internal ribs integrally woven with opposite planar faces so as to form compartments which trap and dissipate sound wave energy passed by at least one of the faces. At least one of the faces, and in some cases selected ones of the internal ribs, are provided with a controlled porosity by being woven of combination yarns, each of which comprises a low-twist core yarn and at least one other low-twist yarn wound around the core yarn. The yarns which are wound around the core yarns prevent the core yarns from flattening excessively during weaving and subsequent resin impregnation and thereby prevent the resin from filling the voids between yarns. In one arrangement each combination yarn is comprised of a core yarn of fiberglass or other appropriate material having a smaller yarn of nylon or other appropriate material served thereon. In an alternative arrangement each combination yarn comprises a plurality of yarns braided onto the outside of a larger core yarn.

in] 3,756,346 1 Sept. 4, 1973 EHEFHFFE 1191.-

rarrrer I541 ACOUSTICAL PANEL I [75] Inventor: Leon Parker, Burbank, Calif.

[73] Assignee: llltco, Irvine, Calif, m 22 Filed: July 3, m2 211 App]. No.: 268,475

[52] us. Cl. 101/33 0, 181/33 a 511 m. n EO-tb 1/99 [58] Field of Search 181/33 GA, 33 on, 181/33 0, as a, as a; 51/144, 149;87l5-7 [$6] 1 References cma UNITED STATES PATENTS 3,147,820 9/1964 Finger 181/33 G UX 3,231,042 1/1966 Chapman 181/33 G UX 3,481,427 12/1969 Dobbs et a1.... 181/33 R 3,502,171 3/1970 Cowan 181/33 R -15 3,565,127 2/1971 Nicely 87/6 X 3,631,667 1/1972 Manocchi 57/144 X 3,700,067 10/1972 Dobbs et al. 181/33 1-1 X Primary Examiner-Richard B. Wilkinson Assistant Examiner-JohnF. Gonzales Attorney-Robert H. Fraser I 1 An acoustical panel, as disclosed, comprises a woven ABSTRACT fabric having internal ribs integrally woven with opposite planar faces so as to form compartments which trap and dissipate sound wave energy passed by at least one of the faces. At least one of the faces, and in some cases selected ones of the internal ribs, are provided with a controlled porosity by being woven of combination yarns, each of which comprises a low-twist core yarn and at least one other low-twist yarn wound around the core yam. The yarns which are wound around the core yarns prevent the core yarns from flattening excessively during weaving and subsequent resin impregnation and thereby prevent the resin from filling the voids between yarns. in one arrangement each combination yarn is comprised of a core yarn of fiberglass or other appropriate material having a smaller yam of nylon or other appropriate material served thereon. In an alternative arrangement each combination yarn comprises a plurality of yarns braided onto the outside of a larger core yarn.

ISCIalmsJDnwhgFigures I L l ield of the Invention The present invention relates to acoustical panels, and particularly to acoustical panels of the type comprising a three-dimensional, integrally woven, resin impregnated fabric. I a

2. History of the Prior Art I 2 rigidity and uniformity are required than such fabric: can provide. I

Om: solution to the problem of maintaining adequati fabric density while at the same time providing npcr tures of sufficient size therein is disclosed in U. 5. Pat No. 3,48 l ,427, Dobbs et al., issued Dec. 2, I969. In "it Dobbs el al. patent at least the face of the acoustica panel is comprised of high-twist yarns having on "It order of 7 twists or turns per inch. The high-twist con Three-dimensional, integrally woven fabric; hav 10 dition of the yarns increases their density and thereb;

been found to provide the basic superstructure for acoustical panels of low cost capable of meeting the dey mands previously satisfied only by very expensive acoustical materials. In the field of aircraft desi for example, three-dimensional woven fabrics when resin impregnated for rigidity have been found to provide relatively inexpensive acoustical panels which can be mounted in critical areas of jet enm'nes and other areas of the aircraft so as to absorb and dissipate substantial amounts of sound. Such acoustical panels typically have a plurality of internal ribs which are integrally woven with opposite faces so as to form compartments therein. At least one of the faces, and in some cases selected ones of the ribs, are provided with a plurality of apertures appropriately dimensioned and configured so as to admit. and thereby trap sound waves within the compartments from outside the face.

The apertures within the various plies of the acoustical panel play a key role in its sound deadening capabilities. On the one hand the face must be provided with a sufficient number of apertures to be of sufficient size so as to pass a considerable volume of sound waves to the inside compartments for dissipation. By the same token the face as well as the other portions of the acoustical panel must have the necessary strength and rigidity so as to be useful for the particular applications in question. A common problem in making a panel which is rigid and strong and .yet adequately apertured arises from the fact that the yarns used to weave the faces and the interconnecting ribs of such fabrics undergo considerable flattening during weaving of the fabric and during subsequent resin impregnationthereof. Such yarns are typically comprised of a plurality of fibers or filaments which have been twisted a few turns per inch to form low-twist yarns. During weaving of typical low-twist fiberglass yarns, for example, a yarn I which is initially generally circular in cross-section and of 0.0l0 inch diameter will be flattened so as to have a width on the order of 0.620 inch upon completion of the weaving. During subsequent resin impregnation and curing the yarns which are subjected to elevated pressures as well as temperatures tend to undergo even further flattening against mandrels inserted therein. As a result the spaces between adjacent yarns in the fabric become extremely small, and during resin impregnation the resin tends to flow over and enclwe such spaces. The practical result is a fabric which while having the necessary strength and rigidity has far too few aperturs or apertures which are too small so as to render the fabric virtually useless as an acoustical member. One obvious solution of this-problem is to weave the fabric with less density in the form of fewer yarns per inch. in this way the yarns can flatten out while still leaving considerable space therebetween. However fabrics woven with such lower densities are typically too flimsy for most applications where greater strength,

their resistance to flattening.

Most yarns of the type used in woven acoustical pan els come in a low-twist condition in which a few turn: or twists per inch have been imparted to them durin the manufacturing process. The few twists per inch im parted to such yarns make them more attractive fron a weaving standpoint, particularly because of the re sulting increased resistance to abrasion and breakage The number of twists per inch in such low-twist yarn: typically varies between about t and 4 with a rough in dustry average being about 3.8 twists per inch.

In order to convert ordinary low-twist yarns intr high-twist yarns having on the order of 7 turns per incl or greater as required by the technique of the Dobbs e al. patent, it is necessary that one of a number of alter native processes be used. One such process involve: placing the yarns in a special machine which twists lllt yarn at a selected rate as it is wound from one spoo onto another spool. Processes such as this can be ex pensive, time consuming, and in some cases are un suited for certain types of yarns such as the more fragih carbon, graphite or other yarns of carbonaceous com position. Moreover many yarns when converted into a high-twist state tend to become unstable and are prom to unravel in erratic fashion making the weaving process unduly difi'icult or in some cases impossible. One possible alternative is to wind together two or morr low-twist yarns in high-twist fashion. However while such a process tends to make certain yarns somewhaw more stable in the high-twist state, it can be time consuming, expensive and still unsuitable for certain yarns A further difficulty lies in the fact that a hightwist con dition achieved by any of the above-noted methods re sults in considerably increased density of the yarn While the increased density is desirable in that it resist: flattening of the yarns it also makes the yarns more re sistant to impregnation by the resin. if impregnation b3 the resin is too incomplete the resulting structure may be unsatid'actory.

BRIEF SUMMARY OF THE INVENTION The present invention eliminates many of the prob lems of the prior art noted above in providing a wover fabric acoustical panel having porbus portions thereol which resist flattening while at the same time providing a suitable fabric density in terms of number of yarns per inch. In accordance with the invention at least one face and in some cases selected ones of the ribs are woven of combination yarns, each of which comprises a core yarn and at least one other yamwound about the core yarn. In one preferred arrangement a yarn of selected composition and size is served onto a core yarn of typically greater size and appropriate composition. In an alternative arrangement a plurality of yarns of appropriate thickness and composition are braided on the outside of a core yarn of considerably larger diameter and of appropriate composition.

V The serving or braiding of small, low-twist yarns on the outside of a larger low-twist core yarn greatly resists flattening of the core yarn during weaving and during suuent resin impregnation and curing. At the same time the slight increase in the overall density of the core yarn is not so great as to resist a thorough impregnation thereof by the resin. The serving or braiding of the core yarns may be accomplished using conventional equipment for this purpose so as to in many cases provide a combination yarn of desired characteristics at a minimum of time and expense. Serving or braiding in accordance with the invention is particularly well suited to fragile yams such as those comprised of carboaaceous materials, making practical the use of such yarns as the core yarns in woven fabric acoustical panels.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings, in which:

H6. 1 is a perspective view of a portion of a woven fabric acoustical panel in accordance with the invention;

H6. 2 is a plan view of a portion of the face of the panel of FIG. I showing a pattern of apertures formed therein;

FIGS. 3A-3C are cross-sectional illustrations of a plurality of yarns during the different states of manufacture of the panel of FIG. 1 illustrating the advantages of the invention;

FIG. 4 is a perspective view of a length of core yarn being served in accordance with the invention; and

FEG. 5 is aperspective view of a length of core yarn being braided in accordance with the invention.

DETAILED DESCRIPTION FIG. I illustrates a portion of an acoustical panel which includes upper and lower generally parallel faces 12 and 14 respectively and a plurality of interconnecting rihs 16. The faces 12 and 14 are generally planar, sheet-like elements integrally woven with the ribs 16. In the example of FIG. I the ribs I6 are parallel to one anomer and extend between and join the faces 12 and 14. As described hereafter selected portions of the panel which may include the upper face I2 and in some cases some or all of the ribs 1'5 have a plurality of apertures which extend therethrough and which serve to pass sound waves into and between internal cements 18 formed by the ribs 16 and the faces I2 and 14. A

The faces 12 and I4 and the ribs 16 are comprised of an integrally woven fabric which is resin impreghated and cured for strength and rigidity. Integrally woven fabrics of this general configuration as well as the techniques and materials used to resin impregnate and cure them are well known in the art. One example of such a fabric and the technique for weaving the same is disclosed in U. S. Pat. No. 3,538,957, Rheaume, issued Nov. 10, I970.

A portion of the upper face 12 of the acoustical panel 10 is illustrated in FIG. 2. As seen in FIG. 2 the face I2 includes a plurality of warp yarns 20 ii rwoven with a plurality of fill yarns 22 in convention fashion. The face 12 is provided with a sufficient number of the 4 yarns 20 or 22 per inch thereof so as to achieve a satisfactory density. At the same time the weave of the face I2 is loose enough so as to define a plurality of apertures 24 between the various warp and fill yarns 20 and 22. The fabric portion illustrated in FIG. 2 could also comprise part of the bottom face 14 or the ribs I6 which are similarly interwoven from warp and fill yarns.

During weaving of the acoustical panel 10 the warp yarns 20 and the fill yarns 22 undergo considerable fiattening. This greatly reduces the size of the resulting apertures 24. When the various yarns 20 and 22 are thereafter impregnated with resin and cured the resulting pressure increase which typically accompanies the curing process may cause even further flattening of the yarns 20 and 22 against mandrels inserted in the compartments 18 so as to reduce the size of the apertures 24. If the apertures 24 become too small the resin tends to cover over and thereby enclose most or all of the apertures 24, rendering the panel 10 useless for acoustical purposes.

In accordance with the invention the various yarns 20 and 22 are comprised of a plurality of low-twist yarns which are interwound such as by serving or braiding so as to substantially resist flattening of the yarns during weaving and subsequent resin impregnation and curing while at the same time maintaining the density of the individual yarns at a sufficiently low level so as to readily accept or absorp the resin during the impregnation process.

FIG. 3A depicts in cross-section four of the warp yarns 20 as they might be positioned relative to one another at the start of the weaving process. While in actual practice the yarns which are made up of plural fibers or filaments are generally other than perfectly circular in cross-section, the various yarns 20 are assumed to be perfectly circular in cross-section and to have a diameter of 0.010 inch for purposes of the present example. In addition the various yarns 20 are assumed to be separated from adjacent yarns by distances very slightly greater than their 0.010 inch diameters.

FEG. 3B depicts the amount of flattening of the yarns 20 which is typically present at the end of the weaving process where low-twist yarns are used. As shown the various yarns 20 have dimensions in the plane of the cloth which are on the order of 0.020 inch or approximately twice the diameters of the various yarns 2% prior to weaving. The resulting apertures 24 between the yarns 20 are of very small size and may even be nonexistent between some of the yarns. When the yarns 20 are thereafter resin impregnated and cured the resin will typically fill the apertures 24 in the example of FIG. 38, resulting in a fabric having an insumcient number of the apertures 24 of adequate size to be useful as an acoustical panel. '1

In the example of FIG. 3B the various yams 20 are assumed to be low-twist yams which have been twisted approximately I to 4 turns per inch of length thereof.

An average figure for the low-twist yarns of the type typically used to form acousti-.':al panels is on the order of 3.8 twists per inch. In any event the term low-twist" as used for purposes of the present invention is deemed to mean something less than about 5 twists per inch.

FIG. 3C depicts the results when the various yarns 20 comprise served or braided yarns in accordance with the invention. As seen in FIG. 3C the various yarns 20 undergo some flattening during weaving and curing but new;

not nearly as much as in the example of FIG. 3B. In accordance with the invention yarns 20 which initially have diameters on the order of 0.010 inch as shown in FIG. 3A are typically flattened to the extent that the dimensions of such yarns within the plane of the cloth are on the order of 0.015 inch after weaving, impregnation and curing. As will be seen this leaves the cloth with apertures 24 of sufficient size so as to pennit resin impregnation and curing without severely reducing the size of or eliminating the apertures 24.

FIG. 4 depicts a portion of the yarn which is being served for use as the warp yarns 20 and the fill yarns 22.

In the example of FIG. 4 a sewing yarn 26 is wrapped around or served on the outside of a core yarn 28. The

. core yarn 28 which is typically on the order of about 0.0l0-0.030 inch thick may be comprised of fiberglass. carbon or any other suitable material. The serving yarn 26 which typically has a diameter considerably smaller than that of the core yarn 28 may be made of any appropriate material such as nylon or Dacron of approximately 30-200 denier. The serving yarn 26 is served onto the core yarn 28 using conventional techniques at an appropriate speed and at an appropriate tension so as to greatly increase the resistance of the yarn to flattening while at the same time making the yarn porous enough toaccept the resin during impregnation. In accordance with the invention it has been found that yarns 26 of the type typically used as described above may be served on the core yarns 28 of the type described above at a rate on the order of 5-15 turns of the serving yarn 26 per inch of length of the core yarn 28 with satisfactory results. Serving at a rate lower than 5 turns per inch produces a combination yarn which may undergo excessive flattening. On the other hand serving at greater than turns per inch typically produces a combination yarn which has more than adequate resistance to flattening but which is too densely bound to properly receive the resin during impregnation.

FIG. 5 depicts an alternative technique of preparing the yarns and 22 in accordance with the invention. In the arrangement of FIG. 5 a plurality of braiding yarns 30 are braided onto the outside of a core yarn 32 using any of a number of braiding techniques known in the art. The braiding yarns 30 are of considerably smaller diameter than the core yarn 32 and may comprise, for exampie, fibers of approximately the same I time have adequate resistance to flattening.

As previously noted the techniques of the present invention are particularly advantageous over those of the prior art where relatively fragile yarns are used. Thus it is frequently desired to weave acoustical fabrics of carbonaceous yarns such as those made of carbon, high modulus graphite or low modulus graphite. However the processing of yarns of this type into a high twist state frequently produces a yarn too fragile for successful weaving. In such situations the present invention produces greatly improved results. Thus, on the one hand the techniques of the present invention do not damage or destroy the fragile yarns through twisting or undesirable operations. At the same time the serving or 6 braiding of more durable yarns onto the outside of the fragile yarns greatly increases the resistance of the fragile yarns to abrasion during the weaving process. This is particularly true of the braiding technique of FIG. 5 which covers enough of the outside surface of the core yam so as to greatly resist abrasion of a core yarn of fragile or easily abraided composition.

In the particular example of FIG. 1 the various ribs 16 are generally parallel with each other and form compartments 18 of generally rectangular cross-section. However other fabric configurations can be used in accordance with the invention such as those in which the internal ribs extend in zig zag fashion between the op posite faces so as to form compartments of generally triangular cross-section.

As previously noted it is typically desired that one of the faces such as the upper face I2, and in some cases selected ones of the ribs 16, have a degree of openness such as is provided by the invention. This is accomplished in accordance with the invention by weaving such parts of served or braided yarns. By the same token it may be necessary or desirable that other parts of the fabric such as the bottom face 14 and the remaining ribs I6 be generally impervious to sound such as by providing them with little or no openings. This can be accomplished using any of a number of appropriate techniques. One such technique is to use conventional low-twist yarns to the extent possible in weaving those parts which are not to be porous. Thus where the bottom face 14 is to be formed with little or no porosity, conventional low-twist yarns which have been neither served nor braided in accordance with the invention are used as both the warp yarns and the fill yarns of the face 14. Such yarns undergo substantial flattening so as to produce little or no porosity in the finished product..Sirnilar considerations apply to the ribs where at least the till yarns and in some cases the warp yarns of those ribs to be formed with little or not porosity are comprised of conventional low-twist yarns.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

- What is claimed is:

I. An acoustical panel comprising a woven fabric having a generally planar face portion and a plurality of internal rib portions integraily woven with and extending-from the face portion to form acoustical compartments within the fabric, at least the face portion being woven'of combination yarns, each of which comprises a core yarn and at least one other yarn wound around the core yarn.

2. The invention defined in claim 1, wherein at least some of the rib portions are woven of the combination yang,

3. The invention defined in claim .1, wherein each of the combination yarns comprises a core yam having a serving yarn served about the outside thereof.

4. The invention defined in claim I, wherein each of the combination yarns comprises a core yarn having a plurality of braiding yarns braided about the outside thereof.

5. The invention defined in claim 1, wherein each of the core yarns has between 1 and 4 twists per inch of length thereof.

Iv L.

' new rarr:

' 6. The invention defined in claim 1, wherein the fabyarn at the rate of between and I5 turns per inch 01 8. The invention defined in claim 7, wherein each of the core and serving yarns has less than 5 twists per inch of length thereof.

9. The invention defined in claim I, wherein the core yarn is comprised of carbonaceous material.

10. The invention defined in claim 7, wherein the serving yarn has a diameter considerably smaller than the diameter of the core yarn and is served on the core length of the core yarn.

II. The invention defined in claim 10, wherein the core yarn comprises fiberglass having a diameter between 0.0l0 inch and 0.030 inch and the serving yarr comprises nylon of between 30 and 200 denier.

12. An acoustical panel comprising a woven fabric having generally planar front and back face portion: and a plurality of rib portions integrally woven with and extending between the front and back face portions, a1 least a portion of the fabric being woven of yams, each of which comprises a core yarn and a plurality of braiding yarns braided onto the outside of the core yarn.

13. The invention defined in claim 10, wherein the 

1. An acoustical panel comprising a woven fabric having a generally planar face portion and a plurality of internal rib portions integrally woven with and extending from the face portion to form acoustical compartments within the fabric, at least the face portion being woven of combination yarns, each of which comprises a core yarn and at least one other yarn wound around the core yarn.
 2. The invention defined in claim 1, wherein at least some of the rib portions are woven of the combination yarns.
 3. The invention defined in claim 1, wherein each of the combination yarns comprises a core yarn having a serving yarn served about the outside thereof.
 4. The invention defined in claim 1, wherein each of the combination yarns comprises a core yarn having a plurality of braiding yarns braided about the outside thereof.
 5. The invention defined in claim 1, wherein each of the core yarns has between 1 and 4 twists per inch of length thereof.
 6. The invention defined in claim 1, wherein the fabric is resin impregnated.
 7. An acoustical panel comprising a woven fabric having generally planar front and back face portions and a plurality of rib portions integrally woven with and extending between the front and back face portions, at least a portion of the fabric being woven of yarns, each of which comprises a core yarn and a serving yarn served on the outside of the core yarn.
 8. The invention defined in claim 7, wherein each of the core and serving yarns has less than 5 twists per inch of length thereof.
 9. The invention defined in claim 7, wherein the core yarn is comprised of carbonaceous material.
 10. The invention defined in claim 7, wherein the serving yarn has a diameter considerably smaller than the diameter of the core yarn and is served on the core yarn at the rate of between 5 and 15 turns per inch of length of the core yarn.
 11. The invention defined in claim 10, wherein the core yarn comprises fiberglass having a diameter between 0.010 inch and 0.030 inch and the serving yarn comprises nylon of between 30 and 200 denier.
 12. An acoustical panel comprising a woven fabric having generally planar front and back face portions and a plurality of rib portions integrally woven with and extending between the front and back face portions, at least a portion of the fabric being woven of yarns, each of which comprises a core yarn and a plurality of braiding yarns braided onto the outside of the core yarn.
 13. The invention defined in claim 10, wherein the core yarn is comprised of carbonacEous material. 